The crossed groove principle is old. It is also known as the track steering principle. Prior to this invention, this principle has been applied in the following way:
A ball-guiding groove is made in one half of the universal joint. Another groove is made in the other half. Each groove is considered to have an imaginary line path that is generated by the center of a ball as it moves along the groove. In the assembled condition of the joint halves, the grooves are in such an opposed relationship that their imaginary line paths always intersect at a point, no matter what angularity the joint halves assume to each other. This point of intersection always lies in the homokinetic plane. A ball confined between the grooves tends to occupy the point of intersection. Whether it does so in the positive, predictable manner that is a critical requirement for proper operation of the joint, depends upon the way the grooves are opposed to each other.
If the grooves are opposed in a radial direction, i.e. one on top of the other, the ball must be urged to the line path intersection by additional means, such as a cage. The ball can transmit torque from one joint half to the other in either direction of rotation. Four balls is the minimum that can be used for proper control. In practice, six are used. The foregoing is best exemplified by U.S. Pat. No. 2,046,584 issued to Rzeppa.
If the grooves are opposed in a peripheral direction, i.e. facing each other side by side, the ball is steered positively into the line path intersection without additional means. The ball, however, can transmit torque from one joint half to the other in only one rotational direction. Four balls is the minimum that can be used. In practice, four are used. The foregoing is best exemplified by U.S. Pat. No. 1,522,531 issued to Weiss.
Numerous other designs shown in the Prior Art use the principle in the same manner. It could more precisely be labeled the Crossed Dependent Groove principle, because one groove in one half of the joint cannot, by itself constrain the ball to travel along the line path associated with that half of the joint. It depends upon the cooperation of an opposed groove in the other half of the joint for ball control, and vice versa.
In contrast, this invention introduces the concept of Crossed Independent Grooves. In each joint half, the grooves are so arranged that they constrain the enclosed ball to travel along the line path associated with that half of the joint independently from the grooves constraining the same ball in the other joint half. This results in positive confinement of the torque transmitting ball to the homokinetic plane by grooves alone, with the ball being able to transmit torque in either rotational direction.